The present invention relates to a method and a device for determining motion parameters of a conductive, preferably profiled surface relative to a sensor, with the sensor comprising at least one coil of a coil system for generating an electromagnetic alternating field, and which is subjected, because of the feedback resulting from position changes between the surface and the sensor, to a variation that is determined by means of the coil system.
Methods and devices of the type under discussion are already known from practical operation, and they are of special importance, in particular when a first object moves relative to a second object at a defined distance, as is the case, for example, with magnetic bearings, levitation devices, gear misalignment detection devices, etc.
DE 32 44 420 C2 discloses a distance sensor for a magnetic levitation vehicle. This sensor comprises one transmitting coil and two receiving coils, with the transmitting coil being designed as an elongate flat winding, which extends with its coil axis obliquely to the direction of movement of the magnetic levitation vehicle. This special arrangement reduces in part the so-called slot-tooth ripple. However, this sensor permits measuring only distances in a range from 10 to 15 mm.
DE 199 27 759 A1 discloses a device for magnetically measuring the distance between a toothed, ferromagnetic pole wheel and a magnetically sensitive sensor that is positioned in the direct vicinity of the pole wheel, and which is used to detect the movement of the toothed wheel. The gist of the invention is the use of a permanent magnet, whose pole surface facing the toothed object is adequately large in proportion with the pole wheel module, so that the position of the neutral zone in the permanent magnet remains nearly unaffected by the respective position of the pole wheel teeth. This device could also be used to determine the rotational speed, the speed, and the path of the pole wheel. Disadvantageous, however, in this device is its low accuracy, in particular in the case of relatively great distances between the sensor and the pole wheel.
In a device disclosed in DE 34 09 448 C2, use is made of the magnetic gap-dependent damping of the magnetic alternating field by the eddy current effects in the reaction rail. In this connection, the inductive reactance of the coil system is fully compensated with the aid of a capacitor that is operated in parallel or series connection, and with that, the distance signal is essentially determined from the active resistance of the coil system. A disadvantageous effect in this case is that the measuring accuracy of the entire device is very strongly influenced by the tolerances of the parameters of the coil system and the compensating capacitors, which are unavoidable in the real buildup.
It is therefore an object of the present invention to provide a method and a device of the initially described type for determining motion parameters of a conductive, preferably profiled surface relative to a sensor, wherein it is possible to measure on the one hand a greatest possible distance between a profiled surface and the sensor, and wherein on the other hand the slot-groove ripple, i.e., signal changes, which develop upon moving over the teeth and slots, as well as influences caused by temperature fluctuations are eliminated as much as possible. Moreover, it is an object to enable at the same time a measurement and evaluation of the relative speed between the surface and the sensor.